Method of processing ferrous strip



25, K. OGANOWSKI ETAL 3,429,164

METHOD OF PROCESSING FERROUS STRIP Filed April 8, 1966 INVENTOR KA S/M/IQ OGANOWSK/ 8, MARI UV B. P/EASON,

BY 7%, mad 3% ATTO R N EYS United States Patent C) 5 Claims ABSTRACT OF THE DISCLOSURE Method of processing ferrous strip to produce nonfluting table-flat strip including steps of Working the strip while heated to a specific temperature range, quenching the worked strip, and continuously leveling said strip.

This invention relates to the processing of ferrous strip, and more specifically to the production of a non-fluting table-flat strip. It has been found that the invention has great and particular utility in connection with the processing of metallic coated strip; however, it will be understood that no limitation is intended, and that the invention is equally applicable to the processing of un-coated strip.

The primary object of this invention is the provision of a process for continuously producing non-fluting, table-flat strip with or without alteration of its surface texture.

As used in this specification, table-flat will be used to describe a strip or sheet which, when observed visually, has an imperceptible deviation from a horizontal flat surface. By Way of example, a 48" by 96" sheet would be considered table-flat if the deviation from a horizontal flat surface would be less than 4; inch.

It is well known in the art that te phenomenon known as stretcher strains and fluting are metallurgically the same, the former occurring upon stretching the latter, upon bending. In this application, the phrase non-fluting will be used to describe a ferrous strip which has been so treated as to substantially eliminate the tendency to form flutes or stretcher strains during subsequent forming or handling operations.

In this connection, it should be pointed out that the prior art is aware of various methods of producing a non-fluting" strip. For example, US. Patent No. 2,5 88,439 in the name of Alfred H. Ward teaches a process wherein a metal strip is subjected to what might be termed hot flexing. That is, ferrous metal strip is heated to a temperature within a specified range and passed through a three roll bender. This hot flexing operation is followed by an immediate quench in order to prevent adverse effects on the physical properties of the material.

The above noted Ward patent also describes other expedients of the prior art for producing a non-fluting strip. These include such cold working steps as temper rolling or roller leveling. While strip which has been subjected to roller leveling may be termed non-fluting, it will be understood that the roller leveling oper-ation actually causes fiuting in a closely spaced and uniform pattern.

According to the prior art, non-fluting table-flat strip could be produced, but only in a two step operation. That is, by following the teachings of the above noted Ward patent, or of US. Patent 2,797,476, in the name of Tadeusz Sendzimir, a manufacturer obtains a non-fluting strip. This strip is then coiled, usually cut into sheets, and then subjected to any of the conventional processes and equipment designed for producing flat stock. As is well known, such conventional equipment includes both the roller levelers, and the stretcher levelers.

Roller leveling is designed to produce table-flat strip, but the desired result is often not achieved. In the first place, successful operation of a roller leveler requires a high degree of skill on the part of the operator, and re quires continuous attention. In the second place, if the strip is too un-level, going in, the roller leveling operation cannot effect a full correction. It is therefore to be preferred that a continuous stretcher leveling step be used.

In achieving the primary object set out above, the inst-ant invention will permit the production of non-fluting table-flat strip at a lower cost, in view of the elimination of several of the steps necessary according to the prior art, and in the elimination of the attendant equipment.

A further object of this invention is to provide a process for producing strip having the characteristics noted above, which is flexible to the extent that the surface texture of the strip can be altered or not, as desired, and required.

Various other objects and advantages of this invention will become apparent upon consideration of this specification. While the invention is described and illustrated in terms of a single exemplary embodiment, it will be understood that no limitation is to be inferred or implied.

The single figure accompanying this specification is a schematic illustration of a processing line according to the teachings of the invention.

Briefly considered, this invention contemplates a process for the continuous treatment of a ferrous met-a1 strip which includes the steps of first working the strip to the extent that its tendency to form flutes or stretcher strains is substantially eliminated, and thereafter continuously leveling the strip.

According to the preferred practice of the invention, the tendency of the strip to formflutes will be substantially eliminated by a hot flexing operation followed by an immediate quench. The stock as thus treated is then passed into a continuous stretcher leveling arrangement. The resulting product is a table-flat strip free of stretcher strains.

Referring now to the single figure accompanying this application, the strip to be treated is indicated at 10. It Will be understood that prior to the practice of the in stant invention, the strip can be treated in any desired way. According to preferred practices of the invention, the strip will have been coated with one of the Well known, conventional coating metals according to the well known Sendzimir process described in Us. Patent No. 2,110,893.

The strip 10 is first subjected to a hot flexing operation on the three roll bender 12 in order to stress at least the outer fibers of the strip through their yield point. The temperature range for the flexing operation is 400 F. to 650 F., and it will be understood that the strip can be brought to this temperature in any conventional way. In certain cases, the residual heat from the hot coating operation will be sufficient.

Since the stresses applied must be sufficient to cause yielding in the outer fibers of the strip, the diameter of the rolls in the bender 12 is critical with respect to strip gage. Experimentation has shown that the maxi-mum roll diameter which can be used successfully is 525 times the strip thickness. As a practical matter, the maximum factor would be 500.

As briefly indicated above, the hot flexing operation is carried out at a temperature in the range of substantially 400 F. to 650 F. The lower temperature limit for the flexing operation has been found to vary in an exponential relationship with the degree of strain introduced by the flexing rolls. This relationship may be expressed by the following formula:

Log D/G=3.90.003t

Where D=diameter of flexing rolls, G=strip gage,

t=-F. (minimum temperature to prevent breaks on flexing rolls).

The upper temperature limit for the hot flexing operation is fixed by the ability to quench the strip before aging occurs. That is, the hot flexing step if followed immediately by quench cooling as schematically shown at 14. This quench cooling should be sufficient to reduce the temperature of the strip to less than 150 F.

It will be apparent that in order to facilitate continuous operation, the diameter of the rolls in the three roll bender 12 will remain constant for all gages of material.

It will also be apparent, therefore, that the temperature range for the hot flexing operations must be varied within the range of 400 F. to 650 F. in accordance with the above discussion.

As briefly explained earlier in this application, the foregoing treatment will substantially eliminate the tendency of the strip to form flutes and stretcher strains.

The continuous stretcher leveling is accomplished by stretching the strip beyond its elastic limit between two tension bridles indicated at 16 and -18. For purposes of illustration, the bridles 16 and 18 each have five rolls, but it will be understood that more or less rolls may be de sirable under varying circumstances. These tension bridles are mechanically coupled together to provide a desired adjustable strip elongation; that is, elongation is determined by the speed differential between bridles. The precise elongation is determined and obtained by engaging the stretch rolls 20 which are disposed ahead of the tension bridle 18.

Upon leaving the tension bridle 18, the strip passes over an inspection table 22. 'It will be observed that at a this stage in the operation, the strip is not under tension. (Note the loop 24 after the inspection table.) This makes it possible to visually, or by the use of instruments, determine, oheck, and control flatness of the resulting product.

The foregoing process will produce the desired prodnet, and will preserve the original finish of the strip. In some cases, however, it is desirable to effect an alteration of the surface. The alteration is eflected by the use of a temper mill, wherein the surface finish is largely controlled by the surface texture of the work rolls. It is well known by the skilled worker in the art that smoothground rolls impart a bright, dense surface finish, while rough-ground or shot-blasted rolls impart a substantially rougher surface. For example, in the case of conventional galvanized (zinc coated) strip, it may be desirable to smooth the surface and substantially eliminate spangles. This is preferably accomplished by the use of smoothground temper rolls disposed as indicated at 26, just ahead of the stretch rolls 20.

It will be recalled from the earlier discussion that a temper roll operation will develop non-fluting properties in the strip. It therefore follows that if surface alteration is desired, and if a temper mill 26 is used, the hot flexing step can be eliminated.

Numerous modifications can be made in the foregoing embodiment without departing from the scope and spirit of this invention. Accordingly, no limitations are intended except insofar as set forth in the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A continuous method of treating coated ferrous metal strip comprising the steps of:

(a) working the strip to the extent that the tendency of said strip to form flutes is substantially eliminated, said working being accomplished by heating said strip to a temperature in the range of 400 F. to 650 F., flexing the strip suflflciently to strain the outer fibers thereof, and quenching said strip; and

(b) continuously leveling said strip, whereby to produce table-flat strip free from flutes and stretcher strain.

2. The method claimed in claim 1 wherein said step of leveling said strip is accomplished by continuously stretching said strip beyond its elastic limit.

3. The process claimed in claim 2 including the step of checking the flatness of said strip by passing said strip without tension over a suitable surface.

4. A process for producing table-flat ferrous strip substantially free from flutes and stretcher strains comprising the steps of:

(a) working said strip while heated to a temperature in the range of 400 F. to 650 '1 (b) immediately quenching said strip to a temperature less than F.; and

(c) continuously stretching said strip beyond its elastic limit.

5. The process claimed in claim 4 including the step of temper rolling said strip while continuously stretching said strip whereby to alter the surface finish of said strip.

References Cited UNITED STATES PATENTS 2,797,476 7/1957 Sendzimir 72365 3,050,847 8/1962 Hill 72365 3,171,464 3/1965 Holtz 72-l60 CHARLES W. LANHAM, Primary Examiner.

R. D. GREFE, Assistant Examiner.

U.S. C1. X.R. 

